Figure 3.1 shows an overview of how a Web page (http://www.example.com/page.html) is
downloaded. The first stage is the DNS lookup (steps 1–4), as mentioned above, where the
user first connects to their ISP’s DNS resolver, which then connects to the Web site’s DNS
server to find the IP address of the requested domain name—‘‘www.example.com.’’ Once
the IP address is determined, a connection is made to the Web server and the desired
page—‘‘page.html’’—is requested (steps 5–6).
Filtering Mechanisms
The goals of deploying a filtering mechanism vary depending on the motivations of the organization deploying them. They may be to make a particular Web site (or individual Web page)
inaccessible to those who wish to view it, to make it unreliable, or to deter users from even
attempting to access it in the first place. The choice of mechanism will also depend upon the
Figure 3.1
Steps in accessing a Web page via normal Web browsing without a proxy.
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Steven J. Murdoch and Ross Anderson
downloaded. The first stage is the DNS lookup (steps 1–4), as mentioned above, where the
user first connects to their ISP’s DNS resolver, which then connects to the Web site’s DNS
server to find the IP address of the requested domain name—‘‘www.example.com.’’ Once
the IP address is determined, a connection is made to the Web server and the desired
page—‘‘page.html’’—is requested (steps 5–6).
Filtering Mechanisms
The goals of deploying a filtering mechanism vary depending on the motivations of the organization deploying them. They may be to make a particular Web site (or individual Web page)
inaccessible to those who wish to view it, to make it unreliable, or to deter users from even
attempting to access it in the first place. The choice of mechanism will also depend upon the
Figure 3.1
Steps in accessing a Web page via normal Web browsing without a proxy.
58
Steven J. Murdoch and Ross Anderson